Problems have been experienced with level sensing in thick walled containers such as the vessel 10 seen in FIG. 1. Notably, a main variable in such environments is growth and shrinkage of the vessel with temperature. In some installations, a source well 12 is suspended from the top end of the vessel, about twenty to thirty inches from the interior vessel wall as seen at 15. Point source(s) are placed in the source well at locations aligned with one or more detectors 22.
The point sources encapsulate the radioactive material distributed over a length of one-quarter to three-quarter inches. Nominally, the position of the radioactive material is centered on the location of the corresponding detector 22. However, expansion and contraction of the vessel 10 tends to misalign a source and detector from the precise alignment at the calibration temperature. If the vessel openings are two inch diameter and the wall is six to twelve inches thick, the source(s) only have to change alignment a fraction of an inch for the source to no longer properly illuminate the detector.
The above-referenced applications disclose a level sensing gauge installable through a single nozzle which addresses the above-noted issue. The single nozzle device maintains alignment of the source and detector, independent of temperature related growth and shrinkage of the vessel, by using the same nozzle in the vessel for the source mounting and the detector mounting.
Although the single nozzle solution described in the above-referenced and incorporated patent filings addresses the thermal alignment problems elegantly, it does require some reconfiguring of the sources and detectors and may not be attractive for some existing installations which are already outfitted with a source well and detectors aligned therewith. Moreover, in some installations it may be desireable not to use a single nozzle for a source and detector, e.g., to permit more independent maintenance or inspection of a detector and source. Thus, there remains a need for additional solutions for nuclear based level sensing large vessels that accommodate for thermal expansion of the vessel.